Tests for asthma
BMJ Group Medical Reference
There are several tests that help your doctor find out what's causing your breathing problems. These tests can help your doctor decide whether you have asthma or another condition.  Your GP can do some of these tests but for others you may need to be referred to a chest specialist at a hospital outpatient clinic.
If your doctor is still unsure if you have asthma, you may be given a trial of asthma drugs (a steroid inhaler or a quick-relief inhaler) to see if they help. If the drugs help you, your doctor can then diagnose asthma and work out a treatment plan.Tests your doctor can doPeak flow test
This test measures how quickly you can breathe out. People with asthma can't breathe out as much air as people who don't have asthma because their airways are narrowed.
Peak flow meters come in several different shapes and sizes. They often look like a baby's bottle. You take a deep breath, then breathe out as hard as you can into a mouthpiece. There is a scale down the side of the meter that measures how quickly you breathe out.
Your doctor may give you this test before and after you take a drug (a bronchodilator) that helps to open up your airways. If you do better in the test after taking the drug, it's usually a sign that you have asthma.
If you have asthma, you may need to do this test at home every day. You'll need to write down the results each day. This helps your doctor see how your asthma changes. It helps your doctor check whether your treatment is working.Tests you may have at an outpatient clinicSpirometry
This is another test to measure how well your lungs are working. It's more accurate than the peak flow test but you can't do it at home. Some GPs have the equipment at their surgery, but others will need to refer you to hospital for the test.
A spirometer is a tube and mouthpiece attached to a computer with a display. You breathe out as hard as you can into the mouthpiece. The spirometer measures two things:
How much air you breathed out in the first second. Doctors call this 'forced expiratory volume in the first second' (or FEV1 for short)
How much air you breathed out during the whole test. Doctors call this your forced vital capacity (or FVC for short).
Your doctor may give you this test before and after you take a drug (a bronchodilator) that helps to open up your airways. This will help your doctor decide whether you have asthma or another condition called COPD.Methacholine challenge test
Most people with asthma get symptoms when they breathe in a chemical called methacholine. If you have asthma and you inhale methacholine, you'll find it harder to breathe. And you'll get lower scores in the other tests for asthma.